In digital processing systems, devices communicate by exchanging data. For that purpose the communicating devices are communicatively connected, i.e., there is a connection between the at least one sender and a receiver. The connection, also known as a communication channel, for example, requires a pathway for transmitting/receiving the data and a data transmission protocol defining the data exchange more specifically.
In conventional data transmission systems a plurality of hardware architectures and a corresponding plurality of data transmission protocols is known, wherein specific hardware architectures can be related to specific transmission protocols and vice versa. For example, protocols may specify to transmit data serially or in parallel. Parallel data transmission protocols specify that, for example, one byte of data is signaled at the same time using eight parallel wires, thus requiring at least eight parallel lines in one transmission channel. In contrast to that data transmission protocols may specify to transmit data serially.
In serial data transmission protocols the bits of the data to be transmitted are signaled one after another using one line or wire, wherein the protocol may specify that the data be packaged into data frames. A data frame may comprise the data to be transmitted and specific protocol data, for example, an address specifying the addressee of the data, a frame identifier and data for ensuring data integrity. For transmitting data between computer devices numerous conventional serial data transmission protocols are known, for example, the Universal Serial Bus (USB) or IEEE 1394 (Firewire).
Besides the well known use in personal computers, serial bus systems have been successfully introduced into various industrial machines for controlling devices therein. Numerous serial data transmission protocols have been developed specifically for controlling devices in machines, for example, known as Controller Area Network (CAN) or the Local Interconnect Network (LIN) or the Inter-Integrated Circuit (I2C). These protocols have been developed to be used, for example, in the automotive industry or automation branch or in so-called embedded systems, for example, for controlling various actuators or systems. While the protocols differ in various specification details they have in common that the bus nodes share at least one line for transmitting/sending and for receiving data, wherein the shared line for transmitting or receiving data may be implemented using a differential signal, for example, as known from the CAN bus physical protocol, or may be implemented using a single line with ground as a reference potential, i.e., as known, for example, from the LIN bus.
Typically the logic for implementing a communication protocol is provided by a microcontroller, wherein the microcontroller provides terminals providing the data to be sent via the bus system and further another interface coupled to a device to control. The microcontroller may further provide other functionality for controlling the coupled device according to data received via the bus or for transmitting data generated by the device. The microcontroller accordingly serves as an interface of the device to the bus system of a specific communication protocol.
The data signals as provided by the microcontroller for sending data via the bus system usually cannot be directly coupled to the physical bus wires, as the logic data provided by the bus do not comply with all requirements of the bus system. For example, when considering the signal integrity the output stage must provide signals of a given voltage level. Accordingly, as conventional microcontrollers are not designed to provide signal levels having a signal integrity compliant with long wires, in conventional bus systems a microcontroller is coupled to the physical bus wires via a transceiver. The transceiver, being a combined transmitter and receiver in a single housing and sharing common circuitry, provides the functionality for applying the signals from the transmit (TxD) terminal of the microcontroller to the bus wire and also for coupling data signaled on the bus wire to the receive (RxD) terminal of the microcontroller. By connecting the TxD and RxD terminals of each bus node via a transceiver to the shared line the line forms a wired-AND.
In structures where bus nodes are located in different voltage domains, in which different reference potentials, i.e., different ground levels, are used, the bus nodes use different voltages as reference potentials. As the bus nodes relate a signal of the RxD or TxD terminal to their individual reference potential, bus signals may have voltages not compliant with the specific node. Accordingly bus systems covering more than one voltage domain additionally require the galvanic separation of the different voltage domains. A decoupler may provide such a galvanic separation, which may be, for example, an optocoupler/opto-isolator or a transformer.
In a bus system comprising a plurality of bus nodes in different voltage supply domains, nodes located in supply domains having a different reference voltage than the bus system are galvanically decoupled from the bus system. Accordingly in conventional systems the RxD and TxD terminals of a microprocessor are each coupled to a decoupling device, the decoupling device is coupled to a transceiver, which in turn is coupled to the bus wires. As the decoupling devices are located between the microprocessors and the transceivers, the microprocessors are galvanically decoupled from the transceivers. All transceivers accordingly can be placed in a single voltage domain, i.e., they may be supplied in a single voltage domain, and each microprocessor can be supplied by any arbitrary different voltage domain.
In conventional bus systems each connection of a node to the bus, e.g., a microprocessor implementing the bus logic functions requires at least a transceiver and, if the node is located in a voltage domain differing from the bus voltage domain, additional decoupling devices for galvanically separating the different voltage domains. Hence there is a need for an improved bus structure.